1. Technical Field
The present invention relates to an image forming apparatus including a line ink jet head having line heads of respective colors arranged at intervals in a sub-scanning direction perpendicular to a main scanning direction, each of the line heads having ink ejecting nozzles arranged in the main scanning direction.
2. Related Art
In the field of ink-jet image forming apparatuses, line ink jet printers have become popular, which can realize high-speed printing by performing image formation (printing) in a main scanning direction in a so-called one-pass operation.
This kind of ink jet printer uses line heads each having ink ejecting nozzles arranged in the main scanning direction. In an ink jet printer capable of printing in two colors or more, particularly, line heads of respective colors are arranged at intervals in a sub-scanning direction perpendicular to the main scanning direction.
A color image is formed on a print sheet by ejecting ink droplets from the nozzles of the line heads of the respective colors when the print sheet passes below the line heads while being conveyed in the sub-scanning direction.
In a color ink jet printer, a landing position shift of any of ink droplets of two colors or more, which are intended to land at the same pixel position on the print sheet, causes a problem of changing the color of the pixel from its originally-intended color tone. Also, it has been known that a landing position shift amount of each ink droplet varies due to a difference in the number of ink drops ejected from the nozzles, and such a variation generates a portion with a color tone change within an image, resulting in deterioration of image quality (see Japanese Unexamined Patent Application Publication No. 2010-173178).
In order to prevent deterioration of image quality attributable to a difference in the number of ink drops ejected, it has been proposed to individually correct the ink ejection timing for each nozzle in accordance with the number of ink drops to be ejected from the nozzle (see Japanese Unexamined Patent Application Publication No. 2010-173178).